I've found that, when rigging and animating humans, sometimes it's easier to connect some parts even if they are hidden. Here's some pictures. Easier to see than explain : Originally, the chainmail arms were a separate mesh just inserted inside the torso. This made rigging more difficult though, as I had to get inside,…
Yeah you can leave them open. Leaving open areas doesn't affect baking (that I know of). You only have to be careful when you are rigging that animation of the mesh doesn't reveal those holes, or empty areas. When you are modeling its a good idea to run a mesh check on each part to make sure the surfaces are connected, and…